Rethinking Aromaticity of Reduced Thienoquinoids: Insights from an S-Pechmann Dye Dianion

Abstract

A dianionic species of thienoquinoid derivative bearing a cross-conjugated γ-thiolactone, so-called S-Pechmann dye, has been synthesized and characterized. Comparative analysis with pentafulvalene dianion with the isoelectronic structure revealed that the S-Pechmann dye dianion exhibits significantly reduced aromatic character due to preferential charge delocalization over the C₄O units. This work provides an in-depth understanding of the fundamental electronic nature of thienoquinoid-based compounds.